Bleed air, or compressed air obtained from within an aircraft's main engines, has traditionally been used to pressurize the aircraft cabin and cargo hold. However, the temperature of this compressed air is typically much higher than required and must be cooled prior to its injection into the cabin. Cooling bleed air in older aircraft required a vapor cycle refrigeration system, which was heavy, expensive and required excessive maintenance. More modern aircraft have eliminated the vapor cycle refrigeration by replacing it with an air cycle system. In addition to an air cycle system, a series of ducts, valves and other heavy equipment requiring intensive maintenance are required to operate this system. Thus, this system is also large, complex, not energy efficient, can overtax the main engine compressors, and results in poor fuel consumption by the aircraft.
Current technological advances have overcome drawbacks presented by bleed air systems by utilizing dedicated separate cabin air compressors to provide compressed air to the aircraft cabin and cargo ventilation systems that is not sourced from the main engines of the aircraft. The pressurized air sourced from these dedicated cabin air compressors is matched to the required pressure so the system is able to operate with a more modest refrigeration system. When warmer air is needed, the compressors can be operated less efficiently to provide warmer air at the same pressure. However, this approach of using additional, large, high speed mechanical equipment, such as separate cabin air compressors, adds excess weight, reliability and complexity challenges to the aircraft.
Given the benefits and drawbacks presented by both types of existing technology, there exists a need for an airplane environmental system that utilizes a single efficient, simple, lightweight, turbomachine that can be controlled to achieve the desired temperature and flow of air to the cabin without the need for additional mechanical equipment.